Construction machines such as an excavator having an electric work element such as a turning mechanism that is driven by an electric motor generally include an electrical energy storage unit including an electrical energy storage device for supplying electric power to the electric work element. Such an electrical energy storage unit including an electrical energy storage device is generally accommodated inside a small chassis. Because heat generated by the electrical energy storage unit and/or heat from the exterior are trapped within the chassis, the atmospheric temperature of the electrical energy storage unit is oftentimes higher than the normal temperature. When the atmospheric temperature of the electrical energy storage unit is high, the electrical energy storage device may be prone to degradation and an electric circuit of the electrical energy storage unit may be prone to failure, for example.
In this respect, a technique has been proposed that involves using an IPM (intelligent power module) in a voltage step-up/down converter that charges/discharges an electrical energy storage device of an electrical storage to prevent a power device of the voltage step-up/down converter (a part of an electric energy storage unit) from overheating (See e.g., Japanese Unexamined Patent Publication No. 2010-226782).